After emerge updated several libraries, I followed up with an "emerge --newuse --deep --update world" and a "revdep-rebuild". Revdep-rebuild is failing on the emerge of knights. The error message states that the build system is building files and then overwriting them, which used to be acceptable, but isn't now. I don't see how to fix what is wrong

One suspicious thing is that the failing emerge lists KDE 4.8 libraries and I just updated to KDE 4.9.

Adjust CMAKE_MODULE_PATH to find FindLibKDEGames.cmake or set
LibKDEGames_DIR to the directory containing a CMake configuration file for
LibKDEGames. The file will have one of the following names:

LibKDEGamesConfig.cmake
libkdegames-config.cmake

-----------------------------------------------------------------------------
-- The following external packages were located on your system.
-- This installation will have the extra features provided by these packages.
-----------------------------------------------------------------------------
* Qt Animation Framework - Support for property animations in Qt

-----------------------------------------------------------------------------
-- Congratulations! All external packages have been found.
-----------------------------------------------------------------------------

-- Looking for dgettext
-- Looking for dgettext - found
-- Found Gettext: built in libc
CMake Warning (dev) at /usr/share/apps/cmake/modules/MacroOptionalAddSubdirectory.cmake:38 (ADD_SUBDIRECTORY):
Policy CMP0013 is not set: Duplicate binary directories are not allowed.
Run "cmake --help-policy CMP0013" for policy details. Use the cmake_policy
command to set the policy and suppress this warning.

is already used to build a source directory. This command uses it to build
source directory

/var/tmp/portage/games-board/knights-2.4.2/work/knights-2.4.2/doc

which can generate conflicting build files. CMake does not support this
use case but it used to work accidentally and is being allowed for
compatibility.
Call Stack (most recent call first):
CMakeLists.txt:43 (macro_optional_add_subdirectory)
This warning is for project developers. Use -Wno-dev to suppress it.